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angular momentum kind of stuff

Sarahisme
in Homework Help

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just a quick phys question

 

A wheel mounted on an axis that is not frictionless is initially at rest. A constant external torque of 50 N . m is

applied to the wheel for 20 s, giving the wheel an angular velocity of 600 rev/min. The external torque is then re-moved, and the wheel comes to rest 120 s later.

Find (a) the moment of inertia of the wheel, and (b) the frictional

torque, which is assumed to be constant.

 

 

and i get (sorry don't have time to write out complete working)

 

a) 60/pi kg.m^2

b) 10 N.m

 

is wrong or right? lol :P

 

Sarah :)

  • Author

acutally i am not so sure maybe it is

a) 300/7pi kg.m^2

b) 50/7 N.m

  • Author

lol this is fairly urgent, :S as in within the next 8 hours :P noooo :S

Looks like your second set of answers are OK.

 

The net torque is the applied + frictional, and you can solve for the two accelerations (pi rad/ s2 for the first part, and pi/6 rad/ s2) for the second.

  • Author

right o thanks swansont :)

 

i just get a little worried about my answers when i am doing them late at night ;)

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